Many photographic materials, particularly color negative films, contain so-called DIR (development inhibitor releasing) couplers. In addition to forming imaging dye, DIR couplers release inhibitors that can restrain silver development in the layer in which release occurs as well as in other layers of a multilayer photographic material. DIR couplers can help control gamma or contrast, can enhance sharpness or acutance, can reduce granularity and can provide color correction via interlayer interimage effects.
To provide suitable inhibition of silver development and the desirable photographic effects thereof, a DIR coupler must release an inhibitor that effectively interacts with silver and/or silver halide during development. In addition to being of the proper structural type, the inhibitor must have the proper degree of hydrophobicity to adsorb efficiently to silver and/or silver halide grains and to retard efficiently silver development. An inhibitor becomes more hydrophobic as the number of carbons in an alkyl chain increases. If the degree of hydrophobicity of the inhibitor is too low it will not effectively inhibit silver development, thus inhibitors with insufficient numbers of carbon atoms or other hydrophopic substituents tend to be inefficient. If the hydrophobicity of a prospective inhibitor becomes too high, its effectiveness also tends to be diminished, since it may become so insoluble in the aqueous developer solution that most of it remains in dispersion droplets rather than diffusing to silver or silver halide particles. Inhibitors that are too hydrophobic also tend to deliver insufficient interlayer interimage, since little inhibitor can diffuse out of the layer in which it is generated.
Triazole releasing DIR couplers are disclosed in U.S. Pat. Nos. 4,182,630, 4,315,069, 4,368,225, 4,833,070 and 5,021,331, Japanese published patent applications Kokai Nos. 07/152,119 A and 07/159,948 A, Czechoslovakian patents 249,556 B1, 249,557 B1 and 261,415 B1 and European patent application 747,415. None of these references teach or suggest the structural features required to achieve all of the desirable properties of the DIR couplers of this invention.